** Changed in: apparmor (Ubuntu)
Status: New => Confirmed
** Changed in: apparmor (Ubuntu)
Importance: Undecided => Low
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https://bugs.launchpad.net/bugs/1339099
Title:
AppArmor file permission 'append' denies file creation
Status in “apparmor” package in Ubuntu:
Confirmed
Bug description:
This bug started as a question, to make sure I know how to computer
before filing a bug:
https://answers.launchpad.net/ubuntu/+source/apparmor/+question/251315
All this work is being done on an up-to-date 14.04 server running
apparmor{-profiles,-utils} 2.8.95~2430-0ubuntu5.
While trying to sort out the appropriate AppArmor bits to control
logging, I'm seeing the file permission 'append' deny create access to
a file, where I would have expected this to not be denied. It also
denies 'file_perm', but it's unclear if this would be expected to
work. I can fix the situation by updating the profile to use the
'write' permission instead of 'append', but this is less than ideal.
http://manpages.ubuntu.com/manpages/trusty/en/man5/apparmor.d.5.html
indicates that the 'append' file permission "Allows the program to
have a limited appending only write access to the file."
In addition,
http://wiki.apparmor.net/index.php/AppArmor_Core_Policy_Reference
explicitly states that 'append' grants "permission to create, and
extend a file. The append permission is limited that it only gives
permission for applications to open a file with O_APPEND, it can not
be used to enforce a generic file write is append only."
From
https://en.opensuse.org/Archive:AppArmor_2_3_changes#Minor_Semantic_Changes,
it appears as though granting 'create' permissions to 'append' is new
in AppArmor 2.3.
However, in writing up a simple test program in Go, I'm seeing
AppArmor deny create permissions where 'append' is allowed.
The Go code:
-----
func main() {
logFile, err = os.OpenFile("/opt/test/log/test.log",
os.O_WRONLY|os.O_CREATE|os.O_APPEND, 0644)
n, err := logFile.WriteString("direct write\n")
if err != nil {
fmt.Println(n, err)
}
log.SetOutput(logFile)
log.Println("Log file initialized.")
logFile.Close()
}
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The AppArmor profile:
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#include <tunables/global>
/opt/test/bin/test {
#include <abstractions/base>
/opt/test/log/test.log a,
}
-----
When set to enforce, the program spits out an error:
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% /opt/test/bin/test
0 invalid argument
%
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And AppArmor logs the DENIED message:
-----
kernel: [ 5687.957758] type=1400 audit(1404743687.548:92): apparmor="DENIED"
operation="open" profile="/opt/test/bin/test" name="/opt/test/log/test.log"
pid=7766 comm="test" requested_mask="c" denied_mask="c" fsuid=1000 ouid=1000
-----
When set to complain, the program works as expected (as expected):
-----
% /opt/test/bin/test
%
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And AppArmor logs three calls with which it has an issue:
-----
kernel: [ 5949.505626] type=1400 audit(1404743948.872:98): apparmor="ALLOWED"
operation="open" profile="/opt/test/bin/test" name="/opt/test/log/test.log"
pid=8158 comm="test" requested_mask="c" denied_mask="c" fsuid=1000 ouid=1000
kernel: [ 5949.505643] type=1400 audit(1404743948.872:99): apparmor="ALLOWED"
operation="file_perm" profile="/opt/test/bin/test"
name="/opt/test/log/test.log" pid=8158 comm="test" requested_mask="w"
denied_mask="w" fsuid=1000 ouid=1000
kernel: [ 5949.505758] type=1400 audit(1404743948.872:100):
apparmor="ALLOWED" operation="file_perm" profile="/opt/test/bin/test"
name="/opt/test/log/test.log" pid=8158 comm="test" requested_mask="w"
denied_mask="w" fsuid=1000 ouid=1000
-----
I'm not sure what's going on with the 'file_perm' stuff either -- I
thought that would have required 'chmod', but that doesn't appear to
be the case.
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